High-density interconnections in mobile phones using ACF

Mobile phone is developing towards an information and entertainment device. In addition, it serves as mobile office for the business users offering access to all needed files and services to conduct daily business. To achieve this, mobile phone needs very high performance and high functionality combined with small size and low energy consumption, keeping the total system cost as low as possible. Increasing functionality requires aggressive integration on integrated circuit and printed wiring board level. Modularity offers freedom for the designers, but interconnections between various modules may become a challenge when number of connections increases and high performance with low interference is required. An interesting option for this interconnection dilemma is to replace board-to-board connectors with Anisotropic Conductive Adhesives (ACA) joining the modules directly to each other. Successful execution of board-to-board (flexible or rigid) interconnection using ACA needs careful consideration of design issues, materials selection, and process development. Rigorous reliability testing ensures that the end user can enjoy the mobile phone without hardware problems. This paper compares process and reliability issues with ACF and ACP.